The present invention relates to surface-treated mineral fillers and method for the preparation thereof. The fillers are particularly suitable for making emulsion paints.
It is known to admix fillers, which are considered relatively cheap substances, to working materials such as paints, paper, plastic material and the like in order to increase their volume and/or weight. Also, fillers are often added to improve the usefulness of such materials.
The behavior of fillers in plastic materials, paints, and the like is decisively influenced by the nature of the filler surface. Attempts have therefore already been made to improve the properties of fillers by treating their surfaces with chemical substances.
For instance, German Pat. No. 958,830 suggests a method for treating natural calcium carbonate with surface-active materials wherein the calcium carbonate, in the presence of synthetic and natural fatty acids, amino-fatty acids, acid amides, fatty alcohols, waxes, and resins is ground up in quantities of between 0.1 and 40% at a temperature of at least 80.degree. C. The problems to which said German patent are directed are to prevent the conglomeration of chalk particles and to facilitate the process of blending with plastic polymers and the like.
Surface-treated fillers suggested in the art possess more favorable properties when compared to untreated fillers. However, they still require considerable improvement particularly in terms of their practical technical properties.
An object of the present invention is to improve the properties of fillers and particularly the mechanical properties of relatively coarse fillers. One special purpose of the present invention is to provide a filler through surface treatment which can be used advantageously to make emulsion paints, and particularly to improve the wash and scrub resistance of the paints.
Over many years of comprehensive series of experiments, applicant investigated many groups of chemical substances and individual substances for their effectiveness as surface-treatment agents.
The following groups of substances, respectively, were tested for their effectiveness: silicones, cyclic esters, paraffin oil, polyethylene waxes, monocarboxylic acids (i.e., saturated or unsaturated fatty acids), saturated or unsaturated dicarboxylic acids, dicarboxylic acid esters, aromatic monocarboxylic acids, aromatic hydroxymonocarboxylic acids, polycyclic dicarboxylic acids, higher alcohols, amines, emulsifiable polymers, inorganic silicates, inorganic fluorosilicates, and wetting agents. None of the substances tested yielded an improvement in the wash and scrub resistance of emulsion paints that could be used in practice.
Surprisingly enough, however, it was discovered according to the invention that the problem can be solved by surface-treating the mineral filler with a mixture of saturated and unsaturated aliphatic acids.
It is particularly surprising that the use of the mixtures consisting of saturated and unsaturated aliphatic acids provided the advantages achieved according to the present invention since the use of saturated or unsaturated acids alone did not provide any noteworthy improvements.